Phase-resolved spectroscopic analysis of the eclipsing black hole X-ray binary M33 X-7: system properties, accretion, and evolution
M33 X-7 is the only known eclipsing black hole high mass X-ray binary. The system is reported to contain a very massive O supergiant donor and a massive black hole in a short orbit. The high X-ray luminosity and its location in the metal-poor galaxy M33 make it a unique laboratory for studying the w...
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| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
11 November 2022
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| In: |
Astronomy and astrophysics
Year: 2022, Volume: 667, Pages: 1-23 |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202243683 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1051/0004-6361/202243683 Verlag, lizenzpflichtig, Volltext: https://www.aanda.org/articles/aa/abs/2022/11/aa43683-22/aa43683-22.html 
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| Author Notes: | V. Ramachandran, L.M. Oskinova, W.-R. Hamann, A.a.C. Sander, H. Todt, D. Pauli, T. Shenar, J.M. Torrejón, K.A. Postnov, J.M. Blondin, E. Bozzo, R. Hainich, and D. Massa |
| Summary: | M33 X-7 is the only known eclipsing black hole high mass X-ray binary. The system is reported to contain a very massive O supergiant donor and a massive black hole in a short orbit. The high X-ray luminosity and its location in the metal-poor galaxy M33 make it a unique laboratory for studying the winds of metal-poor donor stars with black hole companions and it helps us to understand the potential progenitors of black hole mergers. Using phase-resolved simultaneous HST- and XMM-Newton-observations, we traced the interaction of the stellar wind with the black hole. We observed a strong Hatchett-McCray effect in M33 X-7 for the full range of wind velocities. Our comprehensive spectroscopic investigation of the donor star (X-ray+UV+optical) yields new stellar and wind parameters for the system that differ significantly from previous estimates. In particular, the masses of the components are considerably reduced to ≈38 M⊙ for the O-star donor and ≈11.4 M⊙ for the black hole. The O giant is overfilling its Roche lobe and shows surface He enrichment. The donor shows a densely clumped wind with a mass-loss rate that matches theoretical predictions. An extended ionization zone is even present during the eclipse due to scattered X-ray photons. The X-ray ionization zone extends close to the photosphere of the donor during inferior conjunction. We investigated the wind-driving contributions from different ions and the changes in the ionization structure due to X-ray illumination. Toward the black hole, the wind is strongly quenched due to strong X-ray illumination. For this system, the standard wind-fed accretion scenario alone cannot explain the observed X-ray luminosity, pointing toward an additional mass overflow, which is in line with our acceleration calculations. The X-ray photoionization creates an He II emission region around the system emitting ∼10 47ph s−1. We computed binary evolutionary tracks for the system using MESA. Currently, the system is transitioning toward an unstable mass transfer phase, possibly resulting in a common envelope of the black hole and the O-star donor. Since the mass ratio is q ≳ 3.3 and the period is short, the system is unlikely to survive the common envelope, but will rather merge. |
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| Item Description: | Gesehen am 27.01.2023 |
| Physical Description: | Online Resource |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202243683 |